Apparatus and methods for necrosing of the endometrium of a mammalian uterus, useful in treating excessive bleeding (menorrhagia) sterilization procedures, and cancer treatments, are known in the art. Thermal and cryogenic treatments have been utilized in such necrosing techniques and typically involve either the direct or indirect application of heat or cold to the tissue to be treated.
In addition to thermal and cryogenic treatments, methods involving application of caustic chemicals within the human body to treat menorrhagia, achieve sterilization and treat cancers also are known. The use of caustic chemicals as locally destructive agents has been attempted but has been limited by concerns about safety and control of the delivery of various agents as well as other shortcomings due to the methods of application, e.g., blind placement of a particular solid chemical. For example, as described by Babcock, W., Chemical Hysterectomy, Jnl. Obstet. & Gyn., Vol. 7, p. 693 (1924), application of gauze strips soaked in a saturated solution of zinc chloride to the uterine walls has reportedly been used to induce amenorrhea, to cause sterility, and to treat tumors. However this procedure has several disadvantages. The application of the gauze strips is a blind procedure, however. The zinc chloride soaked gauze is packed in the uterus until the practitioner feels the cavity is full. The strips are left in place for a predetermined length of time and then removed. Delivery to and removal from the uterine cavity of the caustic gauze strips necessarily entails substantial risk of infection and of contacting the vaginal walls wherein the caustic could damage the vaginal and other tissue that are not the target of the treatment. Accordingly, successful use of this methodology requires substantial skill and experience, limiting the availability of the procedure to women with access to highly trained medical personnel.
Use of caustic agents such as silver nitrate, zinc chloride and copper sulfate has been studied for use in chemical sterilization by chemically cauterizing the fallopian tubes. However, as discussed by Richart, R., Female Transcervical Sterilization, Chapter 3, Harper & Row (1983), even when massive tubal necrosis was achieved with the application of silver nitrate, a significant proportion of fallopian tubes remained open. When compositions for the sustained release of the caustic agents were employed it was found that control over the release of the caustic agents was insufficient to avoid unacceptable side effects. Additionally, use of strong caustic agents such as acids and alkalies would require the concomitant use of equally strong neutralizing agents whose use is also laden with risk. Use of such agents also puts the practitioner in the difficult position of titrating the neutralization of the caustic agent in the patient's uterus and Fallopian tubes.
Neuwirth describes a particularly effective method for treating menorrhagia, which involves administering a silver nitrate-containing paste to the uterine cavity and distributing the paste therein. See, e.g., U.S. Pat. No. 6,197,351; U.S. Pat. No. 6,187,346; U.S. Pat. No. 6,165,492; and U.S. Pat. No. 5,891,457; the relevant disclosures of which are incorporated herein by reference. The silver nitrate causes necrosis of the endometrium, which in turn stops excess uterine bleeding associated with menorrhagia. After treatment, the caustic silver nitrate is effectively neutralized by administering a solution of sodium chloride, usually physiologic saline, to the uterine cavity. Sodium chloride reacts with the silver nitrate to form insoluble (non-caustic) silver chloride. The silver chloride is then flushed out of the uterus along with any loose necrosed tissued present in the uterus.
Delivery of silver nitrate as a paste, as described by Neuwirth, requires some degree of care to ensure that the paste does not come into prolonged contact with tissues that are not in need of cauterization such as the Fallopian tubes. There exists, therefore, a need for improved vehicles for a more precise delivery of silver nitrate to the uterine cavity to implement chemical cauterization of the endometrium. The present invention provides such improved delivery vehicles.